Biology

• Cells have a nucleus and cytoplasm, surrounded by a cell membrane.
• The nucleus controls the activity of the cell.
• The cytoplasm is where the chemical reactions in the cell occur.
• The cell membrane controls what enters and leaves the cell.
• Respiration takes place in structures called mitochondria and structures called ribosomes are involved in protein synthesis.
• Plant cells have an additional layer-the cell wall- that surrounds the cell membrane.
• Cells exposed to light have chloroplasts for photosynthesis.
• Cells often have permanent vacuoles, which are never present in animal cells.
• Eukaryotic - Description of a cell which has a nucleus, eukaryotic cells also have other structures in the cytoplasm which have membranes around them.
• Prokaryotic - Description of a cell which does not have a nucleus - the DNA is free in the cytoplasm.
• Light microscopes use two lenses - the eyepiece and the objective - to magnify images.
• The formula to calculate magnification is:

  magnification = size of image / real size of object
• Magnification - The amount that an image of something is scaled up when viewed through a microscope.
• An electron microscope gives higher magnification and higher resolution.
• Cell structures such as mitochondria and ribosomes can only be seen with an electron microscope.
• The units to describe size of cells are micrometres, millimetres and metres.
• DNA - the molecule that carries genetic information. Is found in the cell nucleus.
• Humans have 46 chromosomes, which can be arranged into 23 pairs.
• A gene is a section of chromosome that controls the production of a particular protein.
• The type of cell division involved in growth is called mitosis.
• Mitosis ensures that the two daughter cells are genetically identical to the parent cell.
• differentiation - when an unspecialised cell becomes a more specialised cell type.
• In the first days of an embryo’s life, all cells are stem cells. These are known as embryonic stem cells.
• Humans have a small number of stem cells that remain as adults, called adult stem cells.
• Because of the potential to differentiate, stem cells can be used to replace damaged or destroyed cells.
• Stem cells may one day be transplanted to treat conditions such as diabetes and paralysis.
• Techniques such as therapeutic cloning may enable scientists to use stem cells with a patients own genes.
• Stem cells in plants, are found in regions called meristems. These are located at the growing points of the shoot and root.
• Meristem cells can be used to produce new plants quickly and economically.
• Meristem cells may be used in preserving plants that might become extinct.
• Diffusion - The movement of particles from regions of high concentrations to low concentration.
• In the body, diffusion is involved in the movement of oxygen and carbon dioxide in the lungs and urea in the kidney.
• In plants, diffusion is involved in moving oxygen and carbon dioxide out and through plant leaves.
• The greater the concentration gradient (the difference in concentration between two regions)the faster the rate of diffusion?
• The rate of diffusion increases at high temperatures because particles can move more quickly.
• The larger the surface area separating two regions, the faster the rate of diffusion.
• Substances move in and out of the bodies of single called and small organism by diffusion.
• As organism increase in size, their surface area does not increase at the same rate- their surface area to volume ratio gets smaller.
• Diffusion rates inside the organism will be too slow to get substances such as food and oxygen to where they are needed and remove waste.
• Large organisms have additional absorbing surfaces, and may have adaptations in their body shape.